1. Technical Field
The present invention is related generally to radio frequency (RF) reception and, more specifically, to an apparatus and method for RF acquisition and tracking.
2. Description of Related Art
Radio frequency (RF) receivers must be designed to acquire and track an incoming RF signal. In an ideal environment, the RF signal travels from a transmitter in a direct line to the receiver. However, in a more realistic setting, the RF signal from the transmitter is reflected or diffracted by various objects and arrives at the RF receiver along multiple pathways. In such a multipath environment, the signal power level fluctuates. In RF receivers synchronization loops, such as phase-locked loops, have a loop bandwidth designed for operation at a desired operating point. However, in a multipath environment, the loop bandwidth of the synchronization loop varies as the signal power level fluctuates. In certain channel conditions, the variation can deviate significantly from the designed operating point, resulting in a performance loss, such as increased acquisition time, smaller pull-in/lock-in ranges, and the like. Conventional solutions to this problem are increased loop bandwidth design or the use of a hard limiter or coherent automatic gain control (AGC) preceding the synchronization loop. However, each of these approaches has design limitations that, under realistic operating conditions, result in degraded performance of the RF receiver.
Therefore, it can be appreciated that there is a significant need for an apparatus and method that can optimize acquisition time and pull-in/lock-in ranges even in a multipath environment. The present invention provides this and other advantages as will be apparent from the following detailed description and accompanying figures.